In general, it is known that a small interfering RNA (hereinafter, referred to as siRNA) has a short double helix structure of 19 to 27 base pairs, which become incorporated with the RNA-induced silencing complex (RISC) and interferes with the expression of the complementary target messenger RNA (hereinafter, referred to as mRNA) in a sequence-specific manner. (Dykxhoorn, D., M. and Lieberman, J. (2006) Knocking down disease with siRNAs. Cell, 126, 231-235).
Since siRNA has an effect that precisely suppresses expression of the target mRNA even in a small amount, attempts for using siRNA for gene therapy related diseases have actively been made.
However, since siRNA is very unstable in vivo, siRNA easily degrades, and since siRNA is negatively charged in physiological condition, it cannot efficiently penetrate a cell membrane, such that it is difficult to apply siRNA for clinical uses.
In order to solve the above problems, in the related art, a method for forming a nano-sized polyelectrolyte complex by electrostatic interaction between siRNA and cationic gene carriers such as cationic peptides, lipid molecules or polymers have been used. This nanoscale complex can protect siRNA from a degrading enzyme and efficiently facilitate its translocation into a biological cell through endocytosis.
However, since siRNA has a low molecular weight (about 15,000 Dalton or less) and a short and stiff double strand structure, in order to form stable and compact polyelectrolyte complex, a strong cationic gene carrier need to be used, which causes a problem for increasing a non-specific cell toxicity.
On the other hand, a hydrogel has a network structure by forming a three dimensional crosslinking process by physically (hydrogen bond, hydrophobic interaction, and van der Waals force) or chemically (covalent bond and metal-ligand coordination) bonding water-soluble polymers. Since the hydrogel structure has a physicochemical property that is suitable for pharmaceutical applications due to high water content, the hydrogel structure has received much attention in the medical and pharmacology fields.
Accordingly, the present inventors have studied a method for using a hydrogel structure that can stably and efficiently deliver siRNA into a biological cell.